Backflow preventer means a device or a method that prevents backflow in a water distribution system. A device or means to prevent backflow into the potable water system. Prevention of the flow of any foreign liquids, gases or substances into the distribution pipelines of a potable water supply; accomplished by an air gap or mechanical backflow obstacle
Back pressure can force an undesirable contaminant to enter potable water piping. Sources of back pressure may be pumps in the water distribution system, boilers, heat exchanging equipment, or power washing equipment. In these cases there may be an almost constant risk of overcoming the static water pressure in the piping. To reduce the risk of contamination, a backflow preventer can be fitted. A backflow preventer is also important when potentially toxic chemicals are used, for instance for commercial/industrial descaling (boilers) or when bleaches are used for residential power washing.
List of Backflow Prevention Devices
Atmospheric Vacuum Breaker (AVB).
Check valve (usually not a legally approved method of backflow prevention).
Chemigation valve (primarily used in agriculture).
Double check valve, or double check valve assembly (DCVA).
Pressure Vacuum Breaker Assembly (PVB).
Reduced Pressure Principle Valve (RPPV or RP device).